1. Field of the Invention
The present invention relates to a dryer with a built-in precision balance for determining the moisture content of material to be weighed. The dryer includes a weighing dish for receiving the material to be weighed. The weighing dish is connected to a load-receiving unit of the measuring cell of the balance. The dryer further includes a heat source arranged above the weighing dish for heating the material to be weighed. During drying, the weighing dish is arranged within the housing. The dryer further has means for making the weighing dish accessible for charging the weighing dish and for weighing the material to be weighed.
2. Description of the Related Art
For determining the moisture content of a product, a sample of the product is dried and the weight of the sample is measured before and after the drying procedure, and possibly also during the weighing procedure. The drying procedure is preferably carried out directly on a balance in order to avoid losses during the manipulation of the material to be dried and to be able to carry out the determination as quickly as possible.
DE-A1-3814959 discloses a moisture measuring device in which several samples are placed on a rotary plate in a stove and are individually placed on a balance for weighing. In such a device, weighing-in must be carried out on a second balance before placing the samples on the plate and before inserting the plate in the stove. In addition, each sample must be identified in order to avoid mix-ups with other samples.
Since the work surfaces in kitchens and in laboratories are usually very narrow, so that by the permanent presence of a balance which is only used occasionally the necessary surface area utilized by this balance cannot be used for other purposes, EP-A-0145665 proposes a household or laboratory balance which is placed in a conventional standard drawer and can be pushed under the work surface of a work table when it is not used. This balance arrangement makes it possible to keep the work surface free even during the weighing procedure because weighing is carried out in the pulled-out drawer in front of the work surface. Simultaneously, it is made possible that the balance does not have to be newly leveled on the work surface before each use. Also, contamination is avoided while the balance is not in use. This known balance is preferably elastically suspended in the drawer, so that impacts during movement of the drawer can be kept away from the balance unit. In order to safely ensure that the balance is switched off in the pushed-in state, additional means are proposed for allowing current only to be supplied when the drawer is in the fully pulled-out position.
Consequently, this known balance arrangement cannot be used for a weighing procedure with a precision balance in a space which is closed off from the surroundings and excludes air flows. On the one hand, the surface of the weighing dish is located immediately below the work surface, so that it is not possible to build up a closed space above the weighing dish and, on the other hand, the balance is not in operation as soon as the balance is pushed in by a certain distance. In addition, the control and display instruments are pushed together with the balance under the work surface, so that these instruments also do not cover the work surface and are protected.
In another already known dryer (METTLER LP 16 "Infrared Dryer"), a precision balance is mounted in the dryer, wherein the weighing dish is located in a stove or drying chamber. The stove chamber is provided with a swivel-mounted cover for charging the weighing dish with the material to be weighed. The heating element is additionally mounted in the cover. An infrared radiator is used in this known drying stove as a heating element. This drying stove meets the requirements with respect to weighing accuracy because weighing-in of the moist material to be dried and weighing of the dried material can take place directly on the balance. However, it is not very easy to charge the weighing dish which is located within the housing and is only accessible through the opening released by the open cover, and, if necessary, to remove any excess material which has been placed on the weighing dish during weighing-in.